I believe that Google can link in-store purchases to online ad exposure for most credit card users in the US. They've done this by doing a deal with MasterCard

I believe that Google can link in-store purchases to online ad exposure for most credit card users in the US. They've done this by doing a deal with MasterCard to integrate sales data cookie data. https://www.bloomberg.com/news/articles/2018-08-30/google-and-mastercard-cut-a-secret-ad-deal-to-track-retail-sales https://www.bloomberg.com/news/articles/2018-08-30/google-an...